The present invention relates to methods and apparatus for connecting work stations in a local area network using ordinary telephone lines.
In a local area network, a number of computer work stations are coupled together to provide a network of computers with increased power and capabilities over a single computer. These network systems typically use a multi-wire cable or a broadband coaxial cable capable of carrying multiple channels. This type of cabling allows high transmission speeds and the use of complex protocols to accommodate the high speeds. Some systems use ordinary two wire telephone lines but are correspondingly slower in operation.
Several different systems are in use for allowing multiple work stations to communicate along a single connecting cable. In the token-ring system, a code number (token) is passed around the network and each station can transmit only when it has possession of the token. Other systems utilize collision detection to determine if two stations have transmitted simultaneously, with each of the stations then retransmitting at a randomly different time to avoid another collision. Alternatively, a central control system can be coupled to each of the work stations in a star configuration to control the flow of data.
Due to the costs of installing special cables for computer work stations, it would be advantageous to be able to use existing phone lines within a building for coupling work stations together. Two major problems need to be solved to accomplish this. First, voice and data must be both accommodated on the same telephone line. Second, the various work stations must be coupled together at the central PBX for the phone lines in a manner compatible with the transmitting system of the work stations on broadband cable if existing work stations designed to operate on broadband cable are to be used. A further problem arises when a network system has a designated master terminal among the work stations with the remaining work stations being slave terminals. The wiring must be done in such a way that the master is properly connected to its appropriate input at a central routing system connected to the PBX. This wiring must be redone each time the master work station is moved from one phone outlet to another.